ATI: http://www.ebuyer.com/product/169034
NVIDIA: http://www.ebuyer.com/product/165582
Did some digging on eBuyer, those are the best two cards I could find for your budget. You could check around on other sites, overclockers etc.

As some of you may know, some retailers a few weeks back were doing a special pre-order deal for Windows 7. In the UK, you could find the Home Premium E edition for £50 and the Professional E for a bit more. I managed to pre-order the Home Premium E edition for £44.99 from PC World which is a pretty good deal IMO. Of course now they've stopped and are doing it for about 80 (Home Premium and 100 and something for the Professional and Ultimate editions.